1. Field of the Invention
This invention is concerned with a quick opening hatch for use on the transfer tube of a nuclear reactor plant. More particularly, the invention is concerned with a quick opening hatch which will reduce the refueling time and operator exposure to radiation.
2. Description of the Prior Art
The time which it takes to refuel a nuclear power plant is very costly because of replacement power which has to be purchased during such time. U.S. Pat. No. 3,298,746 to Desmarchais et al which is directed to a material handling apparatus for transferring the radiated reactor components from one place to another indicates some of the problems in connection therewith.
In the operation of nuclear reactors, it is common to provide a fuel storage pit adjacent to a reactor or containment pit. The fuel pit generally contains water and is sunk into the earth for the handling and storage of irradiated reactor components such as control rods or fuel assemblies. In the refueling of a reactor, irradiated or spent fuel assemblies are transferred from the reactor pit to the fuel pit for temporary storage. This transfer is accomplished under water to protect the operators from the effect of radiation.
When refueling the nuclear power plant, it is necessary to remove a blind flange on the containment side of the fuel transfer tube in preparation for the flooding of the reactor cavity. After the refueling is completed, the reactor cavity is drained and the blind flange is replaced providing the pressure boundary between the spent fuel building or fuel storage pit and the inside of the containment building.
Heretofore, the fuel transfer system of the nuclear reactor supplied by the assignee of this application was furnished with a blind flange closure on the reactor end or containment side building of the transfer tube. The flange is attached to the tube by 20 bolts which must be removed and reinstalled for each refueling. The reinstallation is particularly time consuming since the bolts must be tightened to a prescribed torque in a specified sequence to assure a leak proof seal. Normally, it takes two men about one hour to remove the flange and about two hours to reinstall it.
As is well known, the longer an operator stays in close proximity to radioactive material the greater his radiation exposure. It is preferable to minimize any such exposure below the permissible exposure limits specified by government regulations. Therefore, it is desirable to be able quickly to remove and replace the flange so as to reduce both the refueling time and worker radiation exposure.
It is of particular concern to provide various means, apparatus and systems to perform the operations of fuel transfer as rapidly as possible both to reduce the amount of down time which is required to refuel the nuclear reactor, and more importantly to avoid as much as possible the amount of nuclear radiation to which the individuals involved in connection with fuel transfer are subjected.
The flange assembly heretofore used while good and quite useful does require about one hour to open the hatch and about two hours to close the hatch.
It is well known to provide various door closure mechanisms for securing a door onto a wall opening of undersea vessels. In particular, U.S. Pat. No. 4,121,383 to Holmes et al disclose a door closure mechanism to secure a door to an opening provided in a vessel. The door is provided with a dished configuration and spider-type locking arrangement which moves locking members transversely to the door axis into interlocking engagement with the vessel body. However, this patent is concerned with the provision of a door closure device which is to be used directly to close an opening, and its primary purpose is to provide for means to operate the door closure from either side of the door. There is no teaching that such a door closure mechanism can be used in connection with a nuclear reactor so as to provide for rapid opening and closing of the door closure mechanism. Further, there is no suggestion of an additional safety locking device for retaining the door closure mechanism so as to retain it in its locked condition. Moreover, there is no disclosure of the possibility of remote operation to reduce operator exposure to nuclear radiation.
Another door closure mechanism is disclosed in U.S. Pat. No. 1,416,308 to Silverman et al and this is an early type of closure device to prevent the entrance of water into a particular area. Further, the door closure mechanism here is also operable from either side of the door. This patent is concerned with the locking of water-tight doors in which horizontally movable bolts are connected with a vertically movable member that is threaded onto a shaft to move the bolts transversely and engage outer portion of the edges of the wall surrounding the openings to be closed. The hatch closure includes a ring wheel which abuts against the inside wall with a portion of the hatch overlying the opening, and here also the disclosure is concerned with the locking of the door to prevent water leakage. However, there is no disclosure of a possible application to a nuclear reactor and the provision for tight sealing and removal operations.
U.S. Pat. No. 3,435,794 to Pechacek is also concerned with a two-way pressure door lock assembly in which horizontally movable spring biased rods are connected to shoes that are readily movable, and there is no disclosure of applying such lock assembly to the sealing of a transfer tube for a nuclear reactor.
Closure devices for closing off the transfer tube of a nuclear reactor are disclosed in patents such as U.S. Pat. No. 3,196,082 to Lemesle et al and Desmarchais et al U.S. Pat. No. 3,298,746. However, these are not concerned with the provision of a quick opening and closing hatch assembly nor with a closure assembly which can be applied to the transfer tube of an existing nuclear reactor to provide for the rapid opening and closing.